During the coming year we will continue to study factors which influence the erythropoietin (Ep) content of kidneys and livers. We will determine the effects of hormones, hepatic regeneration, protein deprivation, and alterations in the renin-angiotensin system on this parameter. Also we will attempt to extract erythropoietin from various regions of rat and human kidneys to ascertain the renal site responsible for Ep production. The effect of nephrectomy on hepatic Ep content in rats at various ages will also be studied. Studies will also be continued on the mechanism by which angiotensin II influences extrarenal erythropoietin production. In this regard we will study its effect on hepatic blood flow. We will also attempt to determine the hepatic cell type responsible for Ep production.